In a prospective interventional study, 44 Clomiphene resistant infertile patients were selected from Abolfazl Infertility Clinic of Bushehr University of Medical Sciences. Letrozole was given orally in a dose of 2.5mg, 5mg and 7.5mg, respectively. If the patient displayed no response, the dosage was increased. The size of follicle, endometrial thickness, estradiol, complications and clinical pregnancy rate were evaluated as the final outcome.